/** create by liuhua at 2018年7月4日 下午3:53:31 **/
package com.star.truffle.core.util;

import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.util.HashSet;
import java.util.Set;

/**
 * <p>
 * 名称：IdWorker.java
 * </p>
 * <p>
 * 描述：分布式自增长ID
 * </p>
 * 
 * <pre>
 *     Twitter的 Snowflake　JAVA实现方案
 * </pre>
 * 
 * 核心代码为其IdWorker这个类实现，其原理结构如下，我分别用一个0表示一位，用—分割开部分的作用： 1||0---0000000000 0000000000 0000000000
 * 0000000000 0 --- 00000 ---00000 ---000000000000 在上面的字符串中，第一位为未使用（实际上也可作为long的符号位），接下来的41位为毫秒级时间，
 * 然后5位datacenter标识位，5位机器ID（并不算标识符，实际是为线程标识）， 然后12位该毫秒内的当前毫秒内的计数，加起来刚好64位，为一个Long型。
 * 这样的好处是，整体上按照时间自增排序，并且整个分布式系统内不会产生ID碰撞（由datacenter和机器ID作区分），
 * 并且效率较高，经测试，snowflake每秒能够产生26万ID左右，完全满足需要。
 * <p>
 * 64位ID (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))
 */
public class IdWorker {
  // 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
  private final static long twepoch = 1288834974657L;
  // 机器标识位数
  private final static long workerIdBits = 5L;
  // 数据中心标识位数
  private final static long datacenterIdBits = 5L;
  // 机器ID最大值
  private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
  // 数据中心ID最大值
  private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
  // 毫秒内自增位
  private final static long sequenceBits = 12L;
  // 机器ID偏左移12位
  private final static long workerIdShift = sequenceBits;
  // 数据中心ID左移17位
  private final static long datacenterIdShift = sequenceBits + workerIdBits;
  // 时间毫秒左移22位
  private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

  private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
  /* 上次生产id时间戳 */
  private static long lastTimestamp = -1L;
  // 0，并发控制
  private long sequence = 0L;

  private final long workerId;
  // 数据标识id部分
  private final long datacenterId;

  public IdWorker() {
    this.datacenterId = getDatacenterId(maxDatacenterId);
    this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
  }

  /**
   * @param workerId 工作机器ID
   * @param datacenterId 序列号
   */
  public IdWorker(long workerId, long datacenterId) {
    if (workerId > maxWorkerId || workerId < 0) {
      throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
    }
    if (datacenterId > maxDatacenterId || datacenterId < 0) {
      throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
    }
    this.workerId = workerId;
    this.datacenterId = datacenterId;
  }

  /**
   * 获取下一个ID
   *
   * @return
   */
  public synchronized long nextId() {
    long timestamp = timeGen();
    if (timestamp < lastTimestamp) {
      throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
    }

    if (lastTimestamp == timestamp) {
      // 当前毫秒内，则+1
      sequence = (sequence + 1) & sequenceMask;
      if (sequence == 0) {
        // 当前毫秒内计数满了，则等待下一秒
        timestamp = tilNextMillis(lastTimestamp);
      }
    } else {
      sequence = 0L;
    }
    lastTimestamp = timestamp;
    // ID偏移组合生成最终的ID，并返回ID
    long nextId = ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;

    return nextId;
  }

  private long tilNextMillis(final long lastTimestamp) {
    long timestamp = this.timeGen();
    while (timestamp <= lastTimestamp) {
      timestamp = this.timeGen();
    }
    return timestamp;
  }

  private long timeGen() {
    return System.currentTimeMillis();
  }

  /**
   * <p>
   * 获取 maxWorkerId
   * </p>
   */
  protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
    StringBuffer mpid = new StringBuffer();
    mpid.append(datacenterId);
    String name = ManagementFactory.getRuntimeMXBean().getName();
    if (!name.isEmpty()) {
      /*
       * GET jvmPid
       */
      mpid.append(name.split("@")[0]);
    }
    /*
     * MAC + PID 的 hashcode 获取16个低位
     */
    return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
  }

  /**
   * <p>
   * 数据标识id部分
   * </p>
   */
  protected static long getDatacenterId(long maxDatacenterId) {
    long id = 0L;
    try {
      InetAddress ip = InetAddress.getLocalHost();
      NetworkInterface network = NetworkInterface.getByInetAddress(ip);
      if (network == null) {
        id = 1L;
      } else {
        byte[] mac = network.getHardwareAddress();
        id = ((0x000000FF & (long) mac[mac.length - 1]) | (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
        id = id % (maxDatacenterId + 1);
      }
    } catch (Exception e) {
      System.out.println(" getDatacenterId: " + e.getMessage());
    }
    return id;
  }

  public static void main(String[] args) {
    long time = 1000 * 60 * 10;
    long begin = System.currentTimeMillis();
    Set<Long> set = new HashSet<>();
    IdWorker id = new IdWorker(0, 1);
    
    while (true) {
      long l = id.nextId();
      if (set.contains(l)) {
        System.out.println(".... -> " + l);
      }
      set.add(l);
      if (begin + time <= System.currentTimeMillis()) {
        System.out.println((time / 60000) + "分钟共生成了 " + set.size() + "个ID");
        break;
      }
    }
  }
}
